Press line synchronization

ABSTRACT

Apparatus for controlling a line of power presses of the type including a flywheel driven by a direct current motor and having a clutch for selectively connecting the flywheel to its respective press drive shaft. The disclosed method comprises energizing the motors and rotating the flywheels while the clutches are disengaged. Thereafter, the speed of rotation of the flywheels is monitored and the excitation of the motors is varied to bring all flywheels to the same rotational speed. The crank or eccentric of each press is positioned at a location so that, considering the inertia of the driven parts of each press, simultaneous actuation of the clutches will cause each press to attain the same rotational speed at substantially the same position of rotation. With the presses rotating at the same rotational speed all the clutches are simultaneously actuated and, thereafter, the angular position of each press crankshaft is measured. After a predetermined time period, variation of the excitation of the motors in response to flywheel speed is discontinued and the excitation is varied in a manner to maintain the presses within a predetermined angular position relationship.

United States Patent Roger Sapolsky Saint-Gratien, France [21] AppLNo. 735,768

[72] Inventor [54] PRESS LINE SYNCHRONIZATION 4 Claims, 2 Drawing Figs.

[52] U.S. Cl .s 100/43,

[51] Int. Cl B30b 15/26, H02k 49/04 [50] Field of Search 100/43, 35,

[5 6] References Cited UNITED STATES PATENTS 2,744,213 5/1956 Jaeschke 310/95X 3,092,756 6/1963 Smith 317/6 Primary Examiner-Peter Feldman Att0rneyMeyer, Tilberry and Body ABSTRACT: Apparatus for controlling a line of power presses of the type including a flywheel driven by a direct current motor and having a clutch for selectively connecting the flywheel to its respective press drive shaft. The disclosed method comprises energizing the motors and rotating the flywheels while the clutches are disengaged. Thereafter, the speed of rotation of the flywheels is monitored and the excitation of the motors is varied to bring all flywheels to the same rotational speed. The crank or eccentric of each press is positioned at a location so that, considering the inertia of the driven parts of each press, simultaneous actuation of the clutches will cause each press to attain the same rotational speed at substantially the same position of rotation. With the presses rotating at the same rotational speed all the clutches are simultaneously actuated and, thereafter, the angular position of each press crankshaft is measured. After a predetermined time period, variation of the excitation of the motors in response to flywheel speed is discontinued and the excitation is varied in a manner to maintain the presses within a predetermined angular position relationship.

PATENTEI] JAN26 I971 mvsmoa ROGER SAPO L SKY 7 BY ATTORNEYS.

PRESS LINE SYNCHRONIZATION The present invention is directed toward the press art and, more particularly, to an improved apparatus for synchronizing a line of presses by position control.

The invention will be described with particular reference to its use on a line of metal working presses; however, it will be appreciated the invention is capable of broaderapplication and could be used on a variety of types of press lines.

Press line controls are known which provide working speed synchronization for the different presses in the line; For example, a control system of this type is discussed at pages 965 to 967 of the May 3, 1967 issue of Machinery and Production Engineering. i

In general, the speed synchronization of the type referred to is not completely satisfactory. Normally, in the course of a working cycle, the total work done by each press varies widely, as does the work being done at any point in time. Some presses perform a simple blanking operation, while others are performing a deep drawing operation. These variations tend to produce a loss of position synchronization even though speed synchronization in terms of press strokes per time period is held relatively constant. In the press line described in the above-noted article, this is overcome by continuous operator monitoring and manual readjustment of individual presses. Additionally, controls are provided to stop the press line if any press gets more than 40 out of phase with the line.

Position synchronization can be accurately obtained by using direct current motor drives for the presses. However, since each motor drives a massive inertia flywheel which is clutch coupled to the press crank or eccentric, it must be possible to connect each flywheel to its respective eccentric at a different angular position. This must be accomplished while the flywheels are running at synchronized speeds.

The present invention provides an improved apparatus, for controlling a direct current motor driven press line in a manner which assures speed synchronization of the flywheels up to the point of coupling of the press cranks or eccentrics and a position synchronization thereafter. By the use of the invention it has been found possible to provide accurate synchronization of the press line under a variety of extreme operating conditions. For example, all presses operating without load, all presses operating at maximum load, or one or several presses operating without load and the remainder operating at varying loads up to maximum.

Specifically, according to one aspect of the present invention, there is provided an improved apparatus for carrying out the method of operating a line of presses each including a flywheel driven by a direct current motor-and having a clutch for selectively connecting the flywheel to its respective press drive shaft. The method includes the steps of:

a. with the clutches disengaged, energizing the motors and rotating the flywheels;

b. continuously measuring the speed of rotation of the flywheels and varying the excitation of the motors to bring all of the flywheels to the same rotational speed;

c. positioning the crank or eccentric of each press at a location chosen-so that considering the inertia of the driven parts of each press simultaneous actuation of the clutches will cause each press to attain the same rotational speed at the same position of rotation;

. simultaneously actuating all of the clutches and measuring the angular position of each press; and,

e. after a predetermined time period, discontinuing variation of the excitation of the motors to maintain all the flywheels at the same rotational speed and thereafter varying the excitation of motors to maintain the presses within a predetermined angular position relationship.

In accordance with another aspect of the invention an improved control system is provided for a line of presses each including a flywheel driven by a direct current motor and having a clutch for selectively connecting the flywheel to its respective press drive shaft. The system includes: master control means selectively connectable for monitoring the speed of rotation of each flywheel and varying the excitation of its respective motor to cause the flywheels torotate at a predetermined synchronized speed; first circuit means for generating a first signal indicative of a desired positionalrelationship for each press during its operation; monitoring means connected with each press for receiving said first signal and generating a second signal indicative of the deviation of the actual position of each press from the desired position; second circuit means operable when said master control means is disconnected for varying the excitation of said motors to maintain said desired positional relationship; and, third circuit means for simultane ously engaging the clutches when the flywheels are rotating at a synchronized speed and, if the presses are in the desired positional relationship after a predetermined time period, disconnecting the master control means and connecting the second circuit means.

Accordingly, a primary object of the invention is the provision of an apparatus for controlling a press line in a manner which ensures speed synchronization of the press flywheels prior to connection to their respective presses and position synchronization thereafter.

A further object is the provision of control apparatus of the type described which permits changing from speed synchronization control to position synchronization control and stopping operation if an angular phase difference of greater than 5 appears in the line.

Another object is the provision of apparatus of the type noted wherein changing from speed synchronization to position synchronization cannot take place if any press is more than 5 out of angular phase after a predetermined time period.

These and other objects and advantages will become apparent from the following description when read in conjunction with the accompanying drawing wherein:

FIG. 1 is a circuit diagram, somewhat diagrammatic, showing an embodiment of apparatus capable of carrying out the invention; and,

FIG. 2 is a representative time-angular speed diagram of an operating cycle of a typical press.

Referring more specifically to FIG. 1 there is shown, somewhat diagrammatically, a press line comprised of four I presses l4. As is conventional the loading, unloading, and

transportation of parts between presses is carried out automatically by mechanism not shown which is synchronized with the operation of the presses.

The preses l4 are similar in their major operational and drive features and, accordingly, only press 3 will be described in detail and like reference numerals will be utilized to identify the like parts of the other presses, but differentiated by the use of prime suffixes. And, description of one element is to be taken as equally applicable to all the elements having the same reference numerals unless otherwise noted.

Particularly, press 3 includes a main drive shaft 10 which directly drives, through an eccentric, crank or other mechanical drive connection, the press slide or ram. An inertia flywheel 12 is arranged to be directly connected to shaft 10 through the agency of a conventionalpneumatic clutch 14.

As shown, flywheel 12 is positively driven through a gear drive connection with an individual, variable speed, direct current motor 16 connected up according to the conventional Ward-Leonard system to a direct current generator 18, driven by an alternating current motor 19.

The synchronization of the presses is controlled according to the order introduced by a master clock or controller unit 20. As shown, the master unit 20 includes a small, variable speed direct current motor 22 which has its output shaft 23 directly connected to a conventional magnetic clutch 24 which functions to selectively drivingly connect shaft 23 to a shaft 26 for a purpose hereafter explained. Also connected to shaft 23 and continuously driven thereby is a tachometer generator 28 the output of which is supplied to a line 30 and a comparator 32. Comparator 32 is also supplied with an adjustable reference voltage from a variable, constant voltage output source 34. The output from comparator 30 is, of

course, indicative of the deviation of the actual speed of motor '22 from that set on source 34. This output is applied through controller 36 to vary the speed of motor 22 to bring the output from tachometer generator 28 to the desired level.

The voltage produced by tachometer 28 corresponds to a chosen speed from the range of speeds of which the presses are capable, e.g. from 3 to 30 strokes per minute. This voltage is utilized as a control signal to ensure that all of the flywheels are rotating at the chosen synchronized line speed prior to engagement of the clutches 14. Specifically, the voltage output is supplied through line 40 to the comparators 42 associated with each press. A second voltage indicative of the actual rotational speed of the flywheel 12 is also supplied to comparator 42 through line 44. This voltage can be generated in a variety of ways but is shown as being produced by a tachometer generator 46 directly driven from the output shaft of motor 16. The error output signal from the comparator 42 is supplied through switches 48 and 50 to a voltage sensitive relay or controller 52 which varies the excitation of generator 18 to, accordingly, vary its output in a direction to produce the desired speed for motor 16 and flywheel 12.

As previously mentioned, the flywheels of the entire line are rotated and brought up to a desired synchronized speed of strokes per .minute prior to actuation of clutches l4 and switching of the line to position control operation. Additionally, although not shown, means are preferably provided to prevent the starting up of line knob from being operative until the desired speed is reached.

Before the clutches 14 are actuated to connect the flywheels to the press drive shafts, the press slide and drive shaft for each press must be in the proper predetermined position. This position is not necessarily the same for each press in the line because of the differing inertia of the parts of various presses and the differing work performed by each. The position of these elements is continuously known through the use of a synchronizing receiver 54 positively driven from the press crank or eccentric. The output fromeach synchronizing receiver 54 is continuously supplied to a phase detector 56 through lines 58.

In order to prevent actuation of clutches 16 if any press is more than 5 out of phase, the error signal output from each of the phase detectors 56 is connected to a voltage sensitive relay 60. The output from 60 is in turn supplied to electropneumatic clutch actuator 62 and, if indicative of any press beingmore than 5 out of phase, conventional means prevent actuation of actuator 62.

The above discussed phase or position control of the line which takes place with energization of clutches 16 is accomplished through master unit 20. Referring specifically to the clutch 24 of master unit 20, it is seen that,'when actuated, this clutch functions to directly connect the output shaft 23 of motor 22 with a shaft 66 which simultaneously drives synchronizing transmitters 68 integrally connected to shaft 66. As shown, the output from each transmitter 68, in the form of a phase control reference signal, is connected to a respective synchronizing receiver 54 through a synchronizing differential 70. Differential 70 permits the phase control reference signal supplied to control each press to be placed a predetermined amount out of phase" relative to the reference control signals supplied to the other presses. As previously mentioned, this permits a dephasing" of each press relative to the identical position of the synchronizing transmitter 54 as required by the variations in work being performed in the different presses.

The time required to bring the driven press elements (e.g. the cranks and slides) up to the desired speed is determined by the time of response of the electric coupling controls, the time of response of the clutch actuating units, and the inertia of the driven elements. The time of response of the clutch 24 of master unit is effectively dependent only on its time of response since its mass which must be accelerated is of negligible inertia. Accordingly, the speed rise curves of the driven parts of the presses and those of the magnetic clutch 24 are out of phase. For this reason, the clutch actuation control signal from the clutch actuator which is received by the actuator 82 for magnetic clutch 24 is delayed for a few fractions of a second by time delay relay 84. This provides for the difference in the lag of actuators 86, clutches l4 and the presses relative to the magnetic clutch 24.

In order that the clutches 14 engage relatively uniformly, all of the relays of their actuators 86 and the respective coupling circuits are preferably arranged to have as short a response time as possible. Additionally, the pneumatic clutch actuating circuits should be arranged to permit all of the clutches to engage and accelerate the driven press elements .with accelerations as equal as possible.

However, even with good design of the above elements, rates of acceleration and speed rises of the driven elements of the presses cannot be perfectly synchronous throughout the first moments of clutch engagement. For this reason, the error signals conducted to clutch actuation controller 62 from phase detectors 56 are delayed for a period of, for example, .2 of a second by a time delay relay 88. This permits time for the driven press members to be brought up to speed and into phase as the changeover is made from speed synchronization control to position synchronization control. However, if after the delay period any press is out of phase more than 5 for example, the angular error signal received by clutch control actuator produces immediate disengagement of the clutches 14 and emergency stopping of the line.

After the clutches 14 have been engaged, position synchronization is substituted for speed synchronization. This is accomplished by actuation of speed-position reguiating relay 90 to open switch 48 and close switch 92. Thereafter, the tachometer generator 28 and comparator 32 play no further role in this phase of regulation of the press line. Specifically, the line is now under phase control operation and the position synchronizing reference signals from synchronizing transmitters 66, transfonned to the proper phase relationship in synchronizing differentials 70, and the actual position signal produced by synchronizing receivers 21, are compared at 56 and the corresponding error signal transmitted to the excitation windings of generator 18 to produce the desired position change by variation of voltage to motor 16.

Although not shown, and not of particular importance to the invention, when stopping of the line is undertaken it is preferable that the line rhythm be slowed to approximately 15 strokes per minute. When this speed is reached, an order signal is given through variable voltage source 34,- which deenergizes the press disengaging controls and disengages clutch 24 of master unit 20. Simultaneously, the press brakes are actuated and the speed of the press motors slowed to a speed corresponding to 3 strokes per minute.

The final stopping of the presses may produce out of phases relationships between them. This is detected by the phase detectors 56 and a visual indication given upon angular error indicating dials not shown. Before the line is again started, the presses must be brought to their starting position in synchronism. Preferably, when the presses are in starting position a synchronism start" signal lights up.

It is preferable that the angular error between successive presses also be detected and starting of the line be prevented when this error exceeds 5 or, alternately stopping of the line be provided if it is running. This can be accomplished in conventional manner by the use of additional voltage sensitive relays not shown.

FIG. 2 shows a representative diagram of the operating cycle of one press stroke. The ordinate is graduated in angular speed and the abscissa in units of time. The line represents the difference Wo introduced in the detector 56 by the synchronizing transmitter 68 connected to the master unit, whereas the lines 101-102-103 show the speed fluctuations of the synchronizing receiver 54 connected to the press. As shown by the line 101 the press slows during effective work. The motor then accelerates (connection 102). At the point C of the cycle, the speed of the press overtakes that of the master unit, but the eccentric or crank has lagged angularly to an extent proportional to the surface ABC. Thereafter the speed of the press continues to increase and then falls from D to E.

The surface ABC equals CDE, and consequently, the speed and position synchronism is reestablished at E before the beginning of the following cycle.

It will be seen that the synchronization of a line of presses according to the invention permits great accuracy in the position control without any manual intervention. In continuous operation, the angular difference between each press relative to the master clock is included in the formula:

(5plus A0) and (plus A0) with AO'not being above one degree.

As is apparent this is substantially better than the inevitable dephasings which take place in the presses controlled by an alternating motor with Foucault current coupling. Additionally, the energizing efficiency of the equipment is excellent and any pumping is avoided.

The invention has been described in great detail sufficient to enable one of ordinary skill in the art to make and use the same. Obviously, modifications and alterations of the preferred embodiment will occur to others upon a reading and understanding of the specification and it is my intention to include all such modifications and alterations as part of my invention insofar as they come within the scope of the appended claims.

I claim:

1. An improved control system providing for a line of presses each including a flywheel driven by a direct current motor and having a clutch for selectively connecting the flywheel to its respective press drive shaft, said system includes:

a. master control means selectively connectable for monitoring the speed of rotation of each flywheel and varying the excitation of its respective motor to cause the flywheels to rotate at a predetermined synchronized speed;

' b. first circuit means for generating a first signal indicative of a desired positional relationship for each press during its operation;

c. monitoring means connected with each press for receiving said first signal and generating a second signal indicative of the deviation of the actual position of each press from the desired position; 7

cl. second circuit means operable when said master control means is disconnected for varying the excitation of said motors to maintain said desired positional relationship;

and,

.third circuit means for simultaneously engaging the clutches when the flywheels are rotating at a' synchronized speed and, if the presses are in the desired positional relationship after a predetermined time period, disconnecting the master control means and connecting the second circuit means.

2. The control system as defined in claim 1 wherein the master control means includes a variable speed motor driving a tachometer generator.

3. The control system as defined in claim 1 wherein the third circuit means includes means for disengaging said clutches if said presses are out of position synchronism by more than a predetermined amount.

4. The control system as defined in claim 1 wherein the first circuit means includes means for providing predetermined individual variations in the first signal sent to each respective monitoring means. 

1. An improved control system providing for a line of presses each including a flywheel driven by a direct current motor and having a clutch for selectively connecting the flywheel to its respective press drive shaft, said system includes: a. master control means selectively connectable for monitoring the speed of rotation of each flywheel and varying the excitation of its respective motor to cause the flywheels to rotate at a predetermined synchronized speed; b. first circuit means for generating a first signal indicative of a desired positional relationship for each press during its operation; c. monitoring means connected with each press for receiving said first signal and generating a second signal indicative of the deviation of the actual position of each press from the desired position; d. second circuit means operable when said master control means is disconnected for varying the excitation of said motors to maintain said desired positional relationship; and, e. third circuit means for simultaneously engaging the clutches when the flywheels are rotating at a synchronized speed and, if the presses are in the desired positional relationship after a predetermined time period, disconnecting the master control means and connecting the second circuit means.
 2. The control system as defined in claim 1 wherein the master control means includes a variable speed motor driving a tachometer generator.
 3. The control system as defined in claim 1 wherein the third circuit means includes means for disengaging said clutches if said presses are out of position synchronism by more than a predetermined amount.
 4. The control system as defined in claim 1 wherein the first circuit means includes means for providing predetermined individual variations in the first signal sent to each respective monitoring means. 